KR20120080582A - Shot peening treatment method for steel product - Google Patents

Abstract

A method of performing a short peening (hereinafter abbreviated as "SP") treatment on a workpiece surface of a workpiece, which is a steel product after thermal curing, to significantly improve the durability (especially heat cycle resistance) of the treated surface of the steel product. Provide SP treatment that can be. A method of performing SP treatment on a workpiece that is a steel product after thermosetting, comprising: a first SP treatment for removing a compound layer (white layer) generated by the thermosetting treatment, and a compressive residual stress on the first SP treated surface after the first SP treatment. A second SP treatment is provided, and after passing through the non-destructive inspection on the presence or absence of removal of the compound layer on the treated surface after the first SP treatment, only the passed product performs the second SP treatment.

Description

Shot peening treatment method of steel product {SHOT PEENING TREATMENT METHOD FOR STEEL PRODUCT}

The present invention relates to a shot peening treatment method for steel products which performs a shot peening (hereinafter abbreviated as "SP") treatment for imparting compressive residual stress to a workpiece that is a steel product after thermal curing.

Here, as a thermosetting process, the metal mold | die (steel material) after nitriding (nitrogenation) process is demonstrated as an example. In the die, particularly the die cast die of light alloy (Al or Mg), as the heating and cooling are repeated for each molding, small cracks (heat check) occur. Therefore, the shaping | molding surface of the said mold requires heat cracking resistance (heat stress fatigue cracking property), and high precision.

However, the present invention can also be applied to other forging dies (cold to hot), as well as to steel products such as gears and springs that require high durability.

For reference, in this specification, "Vickers hardness (HV)" is based on "JIS Z 2244".

In addition, the technical term "short peening" includes projection materials (including grit and cut wire) represented by a shot, similarly to "short peening", even if the original "pin peening" is not intended. It also includes the spray processing method (cold processing method) for the purpose of "grinding / polishing" by projecting onto the workpiece.

As mentioned above, in order to prevent thermal stress fatigue crack (heat crack) of a metal mold | die (steel material) as possible, it is well-known to perform SP process which gives a compressive residual stress (for example, patent documents 1-2). Reference).

Patent Document 1 describes that a mold (steel product) after heat treatment is subjected to a plurality of pinning treatments by suitably changing its hardness and particle diameter with a spherical projection material (shot) having a predetermined hardness and particle diameter. (Claim 3, etc.).

Patent Document 2 describes the use of an amorphous projection material (short) having high hardness and low Young's modulus in the peening treatment of Patent Document 1 (claim 3 and the like).

However, both Patent Documents 1 to 2 are forging to press dies (paragraph [0001] of Patent Document 1, paragraph [0002] of Patent Document 2), and die-casting which is an optimal target product of the present invention. It is not intended for the mold. In addition, Patent Literatures 1 and 2 may have any disclosure or suggestion regarding the SP treatment that gives a compressive residual stress after actively removing the compound layer (high carbide layer) generated by heat treatment (thermal curing treatment). Not.

On the other hand, although it is not the technique regarding the SP process with respect to the shaping surface of a metal mold | die, the technique of removing a surface abnormality layer (white layer, a compound layer) in the coil spring and gear which are steel products after nitriding treatment is prior to SP process. 5 and the like. The removal of the surface abnormality layer is for increasing the SP treatment effect of giving a compressive residual stress.

Patent document 3 describes the manufacturing method of the coil spring which SP-processes after removing the white layer of the coil molded article after nitriding treatment (refer Claim 1 etc.). The removal technique of the compound layer (white layer) described in this patent document is not removed by a shot unlike this invention.

Patent Document 4 discloses shot peening after projecting (shorting) a high hardness granular material having a ferrule shape to the tooth bottom and tooth root of the gear after the heat curing treatment including nitriding treatment. The technique is described (claim 1, etc.). In this patent document, the information regarding the durability improvement by the removal aspect of a nitride treatment layer is not described.

Patent Document 5 uses a hard shot particle having a Vickers hardness of 100 or more as a gear tooth surface of a steel gear (steel product) after nitriding, whereby the compound layer is removed to form a diffusion layer of nitrogen on the tooth surface of the gear. Techniques for exposing are described (claims, etc.). What is described in this patent document differs from performing the two-stage process which distinguished clearly the shot peening for compound layer removal and the shot peening of compressive residual stress provision like this invention.

In addition, in the term of "4.2.3 Properties required for surface treatment dies" of pages 103 to 104 of Non-Patent Document 1, the following description is given about the nitriding treatment of die casting dies.

"In the case of the treatment in which the nitride layer is clearly formed, the surface is buckled from the influence of the compressive stress in the nitride treatment layer in the treatment step so that the residual stress is lowered, and then the distribution form becomes the maximum stress. Take it. In addition, when there is little formation of gas nitride, the maximum value of compressive residual stress is taken from the outermost surface, and the distribution form which falls gradually is shown. This state is in the form of a surface treatment having an inclined function, and the die cast dies subjected to the heat cycle have little change in residual stress due to the decomposition of nitride, and the stress gradient of the surface layer changes smoothly even during the heat-cooling heat cycle. The result is good. For reference, in the treatment formed by the thick nitride, it is confirmed that the tensile stress changes with the decomposition of the nitride of the surface during the heat cycle process. Therefore, the nitriding-processing metal mold | die which thickened the nitride part is quick to generate | occur | produce the crack in an operation process, and it is confirmed as a defect in the surface of a metal mold | die. However, in the decomposition process, there is no crack enlargement or progress, and the opening width does not change clearly even if the number of cycles increases.

As described above, at least in the mold, prior art documents relating to the removal of the compound layer by the shot treatment are not seen.

In addition, not only the mold but also steel products including gears and coils, the information for confirming whether or not the compound layer has been sufficiently removed by the short treatment, and whether or not the determination and confirmation means have been established, is sufficient to remove the compound layer. It was not used at the practical level.

Japanese Patent Laid-Open No. 10-217122 Japanese Laid-Open Patent Publication No. 2003-191166 Japanese Patent Laid-Open No. 5-156351 Japanese Laid-Open Patent Publication No. 2002-166366 Japanese Laid-Open Patent Publication No. 2006-131922

Hibara Masahiko "Life measures of die for die-casting" daily industry newspaper, 2003, p103-104

And nowadays, the improvement of heat stress fatigue crack resistance (heat crack resistance) has been desired more in die casting dies and the like.

In view of the above, the present invention is a method of performing shot peening (hereinafter abbreviated as " SP ") treatment to a workpiece surface of a workpiece that is a steel product after thermosetting treatment, and in particular, durability of the treated surface of the steel product (especially, It is an object (problem) to provide an SP treatment method which can significantly improve heat cycle resistance).

Accordingly, the present inventors have used a nitride layer (compound layer) after nitriding and using a high hardness short to acute projection material (grit) in a die casting die or the like prior to shot peening to impart compressive residual stress. Attempts to remove by shot peening.

Then, the inventors of the present invention have sufficiently removed the compound layer in the first shot treatment in the course of closely studying the phenomenon of shot peening in relation to thermal stress fatigue crack (heat crack) of the mold (the traces of the compound layer And the fact that it is not actually observed) has been achieved, and the short peening treatment method of the steel product of the following structure which concerns on this invention was reached.

As a method of performing a short peening (hereinafter abbreviated as "SP") treatment to a workpiece which is a steel product after thermosetting treatment,

A first SP treatment for removing the compound layer generated by the thermosetting treatment;

A second SP treatment for imparting a compressive residual stress to the first SP treated surface after the first SP treatment,

It is characterized by passing a second non-destructive test on the presence or absence of the removal of the compound layer on the first SP treated surface, and performing only the second product.

In the shot peening method of the steel product of the present invention, it is determined whether or not the compound layer has been sufficiently removed by the first SP treatment, and the mold is caused by thermal cracking (thermal stress fatigue) as shown in Examples described later. The occurrence of cracks (heat cracks) can be prevented remarkably compared with the related art. For example, as shown in Examples described later, even if the first SP treatment is insufficient, if it is insufficient, the number of cracks (cracks) stays at about 1/4 compared to the case where the first SP treatment is not performed. When completely removed by the first SP treatment, the number of cracks is about 1/30 (see FIG. 10).

As a result, the problem that thermal cracking (thermal stress fatigue cracking) due to thermal cycling occurs can be solved as stably as possible.

The rejected products after the pass / fail determination may be collected and arranged to perform the first SP process, but the rejected articles may be returned to the first SP process continuously.

It is preferable to perform the said passability determination by the non-destructive inspection method by an eddy current sensor. There is an advantage that determination of all the workpieces can be made. That is, the inspection of the presence or absence of the compound layer includes the destruction inspection and the non-destruction inspection, but the destruction inspection is not suitable for practical use. This is because, at the practical level, the inspection of all the points is necessary, but the inspection of all the points cannot be performed by the measurement method using the breakdown. For example, when hardness is measured, an indentation will occur at the time of a measurement.

In addition, the number of steps can be reduced, and the apparatus can be simplified by performing inspection by non-destruction by the eddy current sensor. For example, tissue observation can also be considered as a non-destructive test, but there is a problem in that a large number of products, such as a mold, require process water to observe the tissue. In addition, X-ray inspection has a problem that the apparatus becomes too large.

For reference, it is known to measure the compressive residual stress by non-destructive, but the present inventors have confirmed that the compressive residual stress has no correlation with the residual ratio of the compound layer.

In addition, the steel product is not limited to being nitrided, and can be applied to a heat-hardened steel product such as carburizing and quenching.

1 is a flowchart for explaining the shot peening treatment method of the present invention.
FIG. 2: is a model diagram which shows (a) suction type (gravity type), and (B) direct pressure type in the pneumatic acceleration apparatus which is an example of the shot peening apparatus used by this invention.
Fig. 3 is a model diagram showing the principle of the generation of eddy current of the eddy current sensor and the eddy current form in steady state and abnormal state.
4 is a model diagram of detection waveforms of a steady state and an abnormal state at the time of detection.
Fig. 5 is a display model diagram showing 3 sigma determination sources and 2.5 sigma determination sources for determining the presence or absence of compound layer removal by the eddy current inspection apparatus.
6 is a planar model diagram showing an example of the shot peening processing system of the present invention.
FIG. 7 is a front model view of the short peening treatment system of FIG. 6.
8 is a model diagram showing a test method for thermal crack resistance.
9 is a model diagram of a thermal cycle used in the test method.
10 is a cross-sectional photograph showing the results of the thermal crack resistance test.

EMBODIMENT OF THE INVENTION Hereinafter, the form for implementing this invention is demonstrated.

Here, as a to-be-processed product which is a steel material after a thermosetting process, the metal alloy die-cast die (for example, SKD product) after nitriding process is demonstrated as an example.

In the present invention, "nitriding treatment" means that an alloy steel containing any one or more of Al, Cr, Mo, Ti, and V is heated to a low temperature of about 500 ° C in NH ₃ gas, thereby being very hard on its surface. Refers to the heat treatment from which the nitride layer is obtained.

Currently, nitriding methods include gas, salt, and plasma (ion) methods.

Each nitriding treatment varies greatly depending on the heating method of the treatment and the supply of the active nitrogen required for nitriding.

Unlike carburization quenching and high frequency quenching, nitriding is characterized by heating to about 500 ° C. in NH ₃ gas and infiltrating nitrogen on the surface of steel to create a hardened layer of iron nitride. Do not need.

Therefore, unlike the other surface hardening method, the treatment temperature of nitriding is a low temperature of 500-600 ° C. and the treatment of the α-Fe region, so that there is little direct dimensional deformation by nitriding even when nitriding is performed, and the most superficial layer of the nitride layer. Has a stable compressive stress, so it has abrasion resistance and fatigue resistance, does not soften even when the temperature rises to about 600 ° C, is relatively stable against heat, and has good corrosion resistance. It is applied.

The gas nitriding method is to obtain a hardened diffusion layer on the surface of a steel by diffusion of active nitrogen.

[Formula 1]

In the reaction, N in the generated gas generated by decomposition of the NH ₃ gas is diffused in the steel to obtain a nitride layer.

The steel also absorbs very small amounts of molecular nitrogen (N ₂ ), which is only around 0.0005%. Therefore, you may think that it does not nitride at all with molecular nitrogen. NH ₃ easily decomposes at the treatment temperature of nitriding, and thus N generated diffuses into the steel to form nitride. Alloy steel containing metal elements such as pure iron, carbon steel or Ni-Co does not harden even when nitrided, but alloy steels containing metal elements such as Al, Cr, Mo, Ti, and V harden to form a stable hard nitride. That is, the remarkable increase of hardness is confirmed for the alloy steel of the metal element which combines with N and produces | generates high hardness nitride.

In other words, the nitriding method is a phenomenon of hardening not by hardening due to the change of structure but by remarkably hardening by making nitride with high hardness, so that it is not necessary to quench, unlike quenching or the like, even after nitriding treatment.

Here, the "compound layer (white layer)" refers to a layer mainly composed of nitride, carbide, carbonitride, etc. formed near the surface than the diffusion layer of nitrogen, and has a very hard and soft characteristic.

In addition, as shown in FIG. 1, the SP treatment of the present invention basically imparts compressive residual stress to the first SP treatment to remove the compound layer (white layer) and the first SP treatment surface after the first SP treatment. The second SP treatment is included, and after passing through a non-destructive inspection with or without compound layer removal by the first SP treatment, only the passed product is subjected to the second SP treatment.

Here, "the 1st SP process" is hard and sharp like an alandum or a carborandum for the purpose of cutting out the compound layer (white layer) of the surface produced | generated when nitriding is performed. It is a process performed using a shape projection material (grit, cut wire) or a high hardness spherical projection material (short).

When removing the compound layer on the surface by the first SP treatment, it is necessary to select the hardness, the particle diameter, and the projection speed of the projection material so as not to remove even the diffusion layer located below the compound layer. For example, the hardness of the projection material is suitably from the range of Vickers hardness (JISZ2244) HV1200-3000 (preferably HV1700-3000), particle size number (JISR6001) 20-220 (preferably 30-100). Select. In addition, the projection speed is appropriately selected from the range of 0.05 to 1 MPa (preferably 0.1 to 0.5 MPa) as the projection air pressure when the projection material is projected using, for example, an pneumatic accelerator.

"2nd SP process" is a shot peening process for the purpose of providing compressive residual stress. The shot used for the 2nd SP is a general purpose pinning shot, for example, hardness HV500-1200 (preferably HV900-1200), and particle diameter of 0.02-1mm (preferably 0.05-0.2mm) Select appropriately from the range. In addition, the projection speed is appropriately selected from the range of 0.05 to 1 MPa (preferably 0.1 to 0.5 MPa) as the projection air pressure when the shot is projected using the pneumatic accelerator.

For reference, the SP apparatus used for the first SP process and the second SP process is not particularly limited. For example, the projection material is supplied to an air accelerator (suction type (gravity type) or direct pressure type (pressure type)) shown in Figs. Centrifugal accelerators and the like to project the same.

An "eddy current" means the eddy current which arises by irradiating an alternating magnetic flux to a material from a coil (FIG. 3A). This eddy current emits a magnetic flux that negates the magnetic flux from the coil (FIG. 3B), and if the material has an abnormal state of a discontinuity (such as a scratch, crack or distortion), the eddy current is different from the normal state. Otherwise it flows bypassing the part (Fig. 3 (C)). Therefore, when the chemical composition, crystal structure, or the like is different from that of the regular product, the output has a different waveform (Fig. 4). Therefore, by reading the change of this output, it is possible to determine whether the determination target has been subjected to the desired process. (Quoted from the MDK sensor measurement principle of Kaisei Engineer's homepage)

Table 1 lists the organization's influencing factors that contribute to conductivity and permeability.

[Table 1]

In Table 1, (circle) indicates that the degree of influence is large. (Circle) shows that an influence is given. × indicates that no influence is given.

Therefore, it turns out that a chemical component has a big influence on conductivity. In addition, it can be seen that the crystal structure, internal stress, and retained austenite have a great influence on the permeability. That is, in the eddy current inspection apparatus, changes in conductivity, crystal structure, internal stress, and retained austenite can be read indirectly.

Therefore, the eddy current sensor measures the tissue state before the first SP treatment at multiple points (for example, 20 parts), and the tissue state after the first SP treatment is similarly measured at multiple points (for example, 20 parts). In this case, a significant difference (with or without compound layer removal) can be determined.

That is, the amplitude difference (voltage) and the phase difference (time) of the current generated from the magnetic flux of the alternating current at a plurality of points of the untreated or unprocessed portion of the finished product. In the display connected to the eddy current sensor by measuring both sides, the random variable (vector) X is μ-nσ <X <μ + nσ (wherein μ: average value and σ: standard deviation, n: 2.5 to The range of the phase difference and the amplitude difference corresponding to ˜3.5) is displayed as a judgment source, and all of the corresponding plurality of points of the processed portion are plotted on the outside of the judgment source. By determining the case as a passable product, the presence or absence of compound layer removal can be easily determined (refer FIG. 5).

That is, when all of the measurement points of a plurality of parts are displayed on the outer side of the judgment source, it can be concluded that the compound layer is in a heterogeneous state (the compound layer is completely removed). The expected value (P: interval probability) that a compound layer is included in each determination source is as follows about n = 2.5, 3, 3.5, respectively.

P (μ-2.5σ <X <μ + 2.5σ) = 0.9879,

P (μ-3σ <X <μ + 3σ) = 0.9973,

P (μ-3.5σ <X <μ + 3.5σ) = 0.9996

Therefore, in order to avoid misjudgment, the judgment source of 3σ is valid, but the judgment source represented by the range of the random variable X suitably selected from n = 2.5-3.5 can also be used.

<Short peening system>

6-7 show an example of an SP treatment system for steel products. The workpiece W and the workpiece are conveyed into the first SP processing chamber 51 of the first SP apparatus 50 by the first conveying apparatus 10 and projected from the projection nozzle 52 to the workpiece W. Ash is sprayed to carry out the first SP treatment.

The workpiece W subjected to the first SP treatment is conveyed from the first SP apparatus 50 to the pass / fail determination device 70 by the first transfer apparatus 10, and the compound layer on the workpiece W surface Determine if it has been properly removed.

The pass / failure determination device 70 includes a probe 71 (measurer) and an analyzer 72. The workpiece W is determined by measuring the surface state of the workpiece W through the probe 71, and it is determined that the compound layer on the surface is properly removed by the second transfer device 20 by the second SP device 60. Is conveyed into the 2nd SP apparatus 61, and a projection material is sprayed from the projection nozzle 62 with respect to the to-be-processed object W, and a 2nd SP process is performed. After completion of the second SP processing, the second conveying apparatus 20 conveys and accumulates from the second SP apparatus 60 to a predetermined position. In this way, a series of shot peening processes are completed.

On the other hand, the workpiece W determined by the pass / fail determination device 70 as a "failure product" in which the compound layer on the surface of the workpiece W is not properly removed is removed from the pass / fail distribution control device 73. The signal is distributed to the rejected product conveyance device 40 by the pass / fail distribution device 30 by the signal, and is conveyed back to the first SP apparatus 50 by the rejected product conveyance device 40 to perform the first SP process. Again, the workpiece W subjected to the first SP treatment is judged by the pass / fail determination device 70 as described above. If the workpiece W passes, the second SP process is performed, and a series of shot peening treatments are completed. .

For reference, each of the projection nozzles 52, 62 is connected to the compressed air supply apparatus 53, 63 serving as a projection power source, and the projection material hoppers 54, 64 project from the hoppers 54, 64. It is connected so that ash can be supplied. In addition, in order to reuse the used projection material, the projection material is circulated through the classification apparatus 55, 65 to the projection material hoppers 54, 64 to enable partial circulation use. In addition, in the figure, "56, 66" is a dust collector.

For reference, the shot peening system is not limited to FIGS. 6 to 7, and can be appropriately changed.

For example, the workpiece W judged as a rejected product by the pass / fail determining device 70 is temporarily accumulated in another place without being directly conveyed to the first SP device 50, and to a certain extent. At the point where the quantity is collected, the first SP process may be performed. In addition, a 1st SP apparatus and a 2nd SP apparatus can also function as it.

Example

Next, this invention is demonstrated in detail based on an Example (verification test of whether a compound layer was removed).

The test piece used SKD61 material (diameter 15 mm x height 20 mm) after gas nitriding process (compound layer thickness: 5 micrometers).

Each condition of 1st SP process-2nd SP process shall be shown in Table 2.

[Table 2]

As the eddy current inspection apparatus, "Magna test D'HF'probe" (Nihon Fester Co., Ltd.) was used.

In the first SP process, the Example performed 30 s processing at a projection amount of 0.56 kg / min, and the Comparative Example performed 15 s processing at the same projection amount.

And the change of the structure | tissue in 20 parts (measurement pitch 5-10 mm) is read by eddy current about the unprocessed product, the comparative example, and each 1st SP processed product of an Example using the said eddy current apparatus, The result is displayed on the two-dimensional coordinates representing the phase difference (time) and the voltage, and the standard deviation (σ) is obtained. The judgment source whose random variable X illustrated in FIG. 5 corresponds to the range of μ-3σ <X <μ + 3σ Is indicated.

Therefore, it was found that the present verification experiment can efficiently determine whether or not the compound layer has been removed.

The presence or absence of a nitride compound layer and the effect that shot peening imparted on the occurrence of thermal stress fatigue cracking were confirmed by performing a thermal crack test.

The thermal crack test is a test for simulating the thermal fatigue of a die cast die which is repeatedly heated and cooled by molten aluminum and a release material, and a cycle of heating and water-cooling in a short time using a high frequency coil is prescribed. It is a test which evaluates the crack which arises in a test piece when collection is repeated. The conceptual diagram of the heat crack resistance test is shown in FIG. 8, and the thermal pattern is shown in FIG.

1) phosphorus nitride state (the compound layer of 5 ~ 10㎛), 2) 1st SP (compound layer removal incomplete: Comparative Example (see paragraph) above) + 2nd SP, 3) 1st SP (Example Each test piece of) + 2nd SP, was prepared, and the number of cracks which generate | occur | produce after giving 10,000-times thermal fatigue was investigated. A large number of cracks can be said to deteriorate the thermal fatigue characteristics. The result is shown in FIG.

10 shows that the number of cracks after the heat cracking resistance test in the nitrided state is 3490, whereas the cracking decreases by performing shot peening. In particular, it can be seen that shot peening after removing the compound layer completely is more effective.

Next, the case where the judgment source corresponding to the range of (mu) -2.5σ <X <μ + 2.5σ was used was verified. As a result, as shown in FIG. 5, the untreated part was not determined as a process site | part. From this, when applied to steel products such as gears and springs, the probability variable X is in the range of μ-nσ <X <μ + nσ in consideration of the required strength and required precision when used. In the judgment source shown, it turns out that it is possible to select the numerical value of n suitably from n = 2.5-3.5.

This application is based on the patent application 2009-227935 for which it applied on September 30, 2009 in Japan, The content forms a part as content of this application.

In addition, the present invention will be more fully understood by the detailed description herein. However, detailed description and specific Example are preferred embodiment of this invention, and are described only for the purpose of description. This is because various changes and modifications are obvious to those skilled in the art from this detailed description.

Applicants have no intention of offering any of the described embodiments to the public, and any of the disclosed modifications, alternatives, which may not be included in the claims within the claims, are part of the invention under the doctrine of equivalents.

In the description of the present specification or claims, the use of nouns and identical directives should be construed to include both the singular and the plural unless specifically indicated or by the context. The use of any of the exemplary or exemplary terms provided herein (eg, "etc.") is merely intended to facilitate describing the present invention, and unless specifically stated in the claims, the scope of the present invention. It does not impose any restrictions.

Claims (8)

As a method of performing a short peening (hereinafter abbreviated as "SP") treatment to a workpiece which is a steel product after thermosetting treatment,
A first SP treatment for removing the compound layer generated by the thermosetting treatment;
A second SP treatment for imparting a compressive residual stress to the first SP treated surface after the first SP treatment,
A short peening treatment method for steel products, wherein the second SP treatment is performed only after passing through a nondestructive test for the presence or absence of the compound layer removal on the first SP treated surface. The method of claim 1,
Moreover, the short peening treatment method of steel products characterized by returning the rejected product after the said passability judgment to a 1st SP process. The method of claim 1,
A non-destructive inspection for use in determining whether the pass is performed using an eddy current sensor, wherein the short peening treatment method for steel products. The method of claim 3, wherein
The pass / fail determination is determined by both the phase difference (time) and the amplitude difference (voltage) of the alternating current at multiple points of the non-processed portion of the processed or unprocessed product in the workpiece. ) And the measurement signal from the eddy current sensor is input to the display circuit connected through the calculation circuit, whereby the random variable X is μ-nσ <X <μ + nσ (wherein μ: mean value σ: standard deviation, n: the range of the said phase difference and amplitude difference which are 2.5-3.5) is displayed as a determination source in two-dimensional coordinates,
A steel product characterized by judging as a pass product the case where all of the measurement point coordinates of the phase difference and the amplitude difference in the corresponding multiple points of the processed part are plotted on the outside of the determination source. Shot peening treatment. The method of claim 4, wherein
A short peening treatment method for steel products, characterized in that the range of the phase difference and amplitude difference where the random variable X is? -3σ &lt; X &lt; 6. The method according to any one of claims 1 to 5,
The steel product after said thermosetting process is a nitriding process of the steel product containing any 1 or more types of Al, Cr, Mo, Ti, and V, The short peening treatment method of steel products characterized by the above-mentioned. The method according to claim 6,
A short peening treatment method for steel products, wherein the steel product is a die for light alloy diecast. As a short peening system used for the method of performing a short peening (hereinafter abbreviated as "SP") processing to the workpiece which is a steel product after a thermosetting process,
A first SP apparatus for use in a first SP treatment for removing a compound layer generated by the thermosetting treatment;
A second SP device for use in a second SP treatment for applying a compressive residual stress to the first SP treated surface after the first SP treatment;
A judgment device for judging whether the first SP-treated surface has a compound layer removed or not;
When the determination in the determination device is a pass, the conveying device for conveying the workpiece to the second SP device and the rejecting device conveying device for conveying the workpiece to the first SP device when the determination is rejected are laid. Short peening processing system of steel products characterized in that there is.

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